The object of the invention is a new advantageous mobile phone accessory for the hands-free function, with the aid of which the characteristics of a mobile phone with a connected accessory are changed into an operating mode associated with the accessory, such as hands-free operation in a car; and an arrangement formed by a cradle and the mobile phone; and further an accessory connector.
From the patent publication WO 95/12961 there is known a system consisting of a number of low directivity microphones and a high directivity microphone based mostly on the pressured difference and realised with a processor. In addition to the low directivity of the separate microphones the system is based on the sound delay from a first microphone to the next one, and on the processing of data which is obtained from different microphones, whereby the processing is based on the delay of the sound.
From the patent publication WO 98/17046 there is known a mobile phone microphone arrangement, due to which the microphone provides an electrical signal corresponding to the user""s voice, in spite of the background noise. The arrangement is based on the use of a pressure difference microphone, so that both the user""s voice and the background noise is directed from the front of the device via a voice opening to the first side of the microphone, and only background noise from the side of the device noise is directed via a noise opening to the other side of the microphone. The major part of the background noise is attenuated by being compensated from the opposite sides of the membrane of the pressure difference microphone. The user""s voice acts on the membrane mainly via the voice opening, so that the microphone output provides a signal corresponding almost only to the user""s voice.
FIG. 1A shows the schematic structure of a known microphone operating by the pressure difference (pressure gradient microphone), and there is shown the microphone frame 1, on the left the first sound opening 1A, on the right a second sound opening 1B, and a membrane 2. The sound via both openings 1A, 1B acts on the membrane 2 so that the membrane provides a signal according to the momentary pressure difference of the sound. FIG. 1B shows the schematic structure of a known pressure microphone, and there is shown the microphone frame 3, a single sound opening 3A and a membrane 4. All sounds coming through the sound opening 3A act on the membrane 4. The membrane 4 located centrally in the microphone 3 generates a signal which corresponds only to the pressure supplied through the opening 3A.
There is also a known mobile phone which contains both a pressure microphone and a pressure gradient microphone in order to attenuate interference caused by the wind.
There is also a known mobile phone 5 according to FIG. 2, which shows a loudspeaker 6, the voice and noise openings 7a, 7B of a pressure gradient microphone, an end plate 8, a keypad 9 defined by the broken lines, and a display 10. In this mobile phone 5 the openings 7A, 7B of the pressure gradient microphone are close to each other restricted by the small end plate 8 at the lower end of the device 5. When the user talks and keeps the device 5 at the side of his head the voice acts causing a pressure difference between the microphone openings 7A, 7B. Thus the microphone generates a signal corresponding to the voice, but the noise directed simultaneously to both openings does not cause any signal. Further a noise from a direction opposite to that of the voice can be attenuated in a known way by data processing.
A problem in known arrangements is the use of a telephone provided with a noise suppression arrangement in such situations where the telephone is not held at the side of the head. Then the noise suppression attenuates also the voice. Such situations are for instance the hands-free function when the device is in a cradle, such as in a car cradle or in table-top cradle.
The object of the invention is to present a solution for a mobile phone containing a noise suppression arrangement, by which the mobile phone advantageously can be used both close to the head and also in a cradle or connected to an accessory, without attenuating the voice and particularly the low frequencies of the voice.
The invention relates to a mobile phone accessory, particularly for such a mobile phone hands-free application which consists of noise suppression based on a pressure gradient microphone having at least two sound openings, whereby the characteristics of the mobile phone are changed with the aid of the accessory. According to the invention the accessory comprises a projection for covering at least one of the at least two openings in the cover of the mobile phone when attached to the mobile phone.
The invention relates also to an arrangement for the hands-free function of a mobile phone, which arrangement includes a mobile phone having a noise suppression based on a pressure gradient microphone with at least two sound openings, and an accessory due to which the characteristics of a mobile phone attached to the accessory are changed. According to the invention the accessory comprises a projection for covering at least one of the at least two openings in the cover of the mobile phone when the mobile phone is attached to the accessory.
The invention relates also to a cradle part, thanks to which the characteristics of a mobile phone, which is mounted in the cradle and which contains noise suppression based on a pressure gradient microphone with at least two sound openings, are changed for the hands-free function. According to an advantageous embodiment of the invention the cradle part comprises a bridge or a projection which can be mounted so that it covers at least one of the at least two sound openings when the mobile phone is placed in the cradle, in order to obtain the characteristics of a pressure microphone with a pressure gradient microphone.
The invention relates also to an arrangement for the hands-free function of a mobile phone, whereby the arrangement includes a mobile phone having noise suppression based on a pressure gradient microphone with at least two sound openings, and a connector, thanks to which the characteristics of the mobile phone are changed. According to an advantageous embodiment of the invention the connector connected to the mobile phone comprises a flange for covering at least one of the at least two sound openings of the mobile phone in order to obtain the characteristics of a pressure microphone.
The invention saves the costs of a particular electronic implementation. The strip covering one of the pressure gradient microphone""s two sound openings will not essentially increase the manufacturing costs and is thus advantageous.
The invention also saves the possessor of the mobile phone from the purchase of a separate table-top cradle when for instance a connector of a battery charger is available to him, whereby the connector includes a flange according to an advantageous embodiment of the invention. The mounting of the connector provides automatically microphone characteristics according to the hands-free function.
The pressure gradient microphone used for noise suppression performs substantially better than a pressure microphone regarding sounds generated in close range, when the case is examined in the light of the interference ratio. However, a pressure gradient microphone has a poor sensitivity to low frequency sounds at longer distances, whereby the interference ratio also deteriorates. An advantage of the invention is that the characteristics of a pressure gradient microphone change so that they are like those of a common pressure microphone, whereby the microphone""s sensitivity increases, particularly at low sounds. No second microphone nor a headset is required thanks to the invention. Advantageous embodiments of the invention are presented in the dependent claims.